The geology of Thurston County and the South Puget Sound basin was sculpted by the Vashon Glaciation over 15,000 years ago. Beneath residential neighborhoods in Olympia, Tumwater, and Rochester lies an unpredictable patchwork of geological strata: dense Vashon glacial till, loose recessional outwash gravels, and expansive clay deposits.
Expansive clay soils contain clay minerals (such as smectite and montmorillonite) that exhibit dramatic shrink-swell characteristics. During our dry, hot Pacific Northwest summers, clay particles lose moisture, shrink, and crack, creating voids beneath foundation footings. When heavy autumn atmospheric rivers arrive, the clay absorbs water like a dry sponge, swelling in volume by up to 10% and exerting tremendous upward heave.
This perpetual seasonal cycle creates 'differential settlement.' A foundation footing that settles uniformly an inch causes minimal damage; but when the south-facing sunny side of your home dries out and drops 1.5 inches while the shaded north side remains stable, the concrete foundation twists under immense rotational shear.
Homeowners typically first notice interior cosmetic clues: diagonal cracks radiating from door and window frames at 45-degree angles, interior doors that suddenly swing open or stick in their jambs, and gaps appearing between baseboards and hardwood floors.
Stopping differential settlement permanently requires bypassing unstable surface soils entirely. Olympia Foundation Repair Pros installs heavy-gauge galvanized steel push piers or helical piers driven 15 to 35+ feet deep through unstable clay and outwash alluvium into load-bearing, impenetrable Vashon hardpan, permanently stabilizing your home.